U.S. patent number 10,940,668 [Application Number 16/227,545] was granted by the patent office on 2021-03-09 for functional layer including layered double hydroxide, and composite material.
This patent grant is currently assigned to NGK Insulators, Ltd.. The grantee listed for this patent is NGK INSULATORS, LTD.. Invention is credited to Naoko Inukai, Sho Yamamoto, Shohei Yokoyama.
![](/patent/grant/10940668/US10940668-20210309-D00000.png)
![](/patent/grant/10940668/US10940668-20210309-D00001.png)
![](/patent/grant/10940668/US10940668-20210309-D00002.png)
![](/patent/grant/10940668/US10940668-20210309-D00003.png)
![](/patent/grant/10940668/US10940668-20210309-D00004.png)
![](/patent/grant/10940668/US10940668-20210309-D00005.png)
![](/patent/grant/10940668/US10940668-20210309-D00006.png)
United States Patent |
10,940,668 |
Yamamoto , et al. |
March 9, 2021 |
Functional layer including layered double hydroxide, and composite
material
Abstract
There is provided a functional layer including a layered double
hydroxide. The functional layer further contains titania.
Inventors: |
Yamamoto; Sho (Nagoya,
JP), Yokoyama; Shohei (Nagoya, JP), Inukai;
Naoko (Nagoya, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
NGK INSULATORS, LTD. |
Nagoya |
N/A |
JP |
|
|
Assignee: |
NGK Insulators, Ltd. (Nagoya,
JP)
|
Family
ID: |
1000005414125 |
Appl.
No.: |
16/227,545 |
Filed: |
December 20, 2018 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20190126588 A1 |
May 2, 2019 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
PCT/JP2017/022905 |
Jun 21, 2017 |
|
|
|
|
Foreign Application Priority Data
|
|
|
|
|
Jun 24, 2016 [JP] |
|
|
JP2016-125531 |
Jun 24, 2016 [JP] |
|
|
JP2016-125554 |
Jun 24, 2016 [JP] |
|
|
JP2016-125562 |
Jan 31, 2017 [WO] |
|
|
PCT/JP2017/003333 |
Mar 27, 2017 [WO] |
|
|
PCT/JP2017/012422 |
Mar 27, 2017 [WO] |
|
|
PCT/JP2017/012427 |
Mar 27, 2017 [WO] |
|
|
PCT/JP2017/012435 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01F
7/00 (20130101); H01M 10/26 (20130101); B32B
9/00 (20130101); C01F 7/02 (20130101); C01G
53/006 (20130101); H01M 50/449 (20210101); H01M
50/403 (20210101); C01G 23/047 (20130101); H01M
50/431 (20210101); C01G 53/04 (20130101); H01M
4/32 (20130101); C01G 23/00 (20130101); H01M
4/244 (20130101); B32B 5/18 (20130101); H01M
50/409 (20210101); C01G 23/04 (20130101); C01G
53/00 (20130101); B32B 9/005 (20130101); B32B
2305/026 (20130101); C01P 2004/03 (20130101); C01P
2006/40 (20130101); B32B 2457/10 (20130101); C01P
2002/22 (20130101); C01P 2002/74 (20130101); C01P
2006/16 (20130101) |
Current International
Class: |
B32B
5/18 (20060101); B32B 9/00 (20060101); H01M
4/24 (20060101); C01G 23/047 (20060101); H01M
10/26 (20060101); C01G 53/04 (20060101); C01G
23/04 (20060101); C01F 7/02 (20060101); C01G
53/00 (20060101); C01G 23/00 (20060101); C01F
7/00 (20060101); H01M 4/32 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1322381 |
|
Nov 2001 |
|
CN |
|
3 015 430 |
|
May 2016 |
|
EP |
|
2001-302944 |
|
Oct 2001 |
|
JP |
|
2003-277646 |
|
Oct 2003 |
|
JP |
|
2005-089277 |
|
Apr 2005 |
|
JP |
|
2010-059005 |
|
Mar 2010 |
|
JP |
|
2010-235437 |
|
Oct 2010 |
|
JP |
|
2013-201056 |
|
Oct 2013 |
|
JP |
|
2014-123431 |
|
Jul 2014 |
|
JP |
|
2015-015229 |
|
Jan 2015 |
|
JP |
|
2015-095286 |
|
May 2015 |
|
JP |
|
2015-520018 |
|
Jul 2015 |
|
JP |
|
2015-535797 |
|
Dec 2015 |
|
JP |
|
2016-084263 |
|
May 2016 |
|
JP |
|
2016-084264 |
|
May 2016 |
|
JP |
|
2017-082191 |
|
May 2017 |
|
JP |
|
2008/075621 |
|
Jun 2008 |
|
WO |
|
2013/118561 |
|
Aug 2013 |
|
WO |
|
2015/098610 |
|
Jul 2015 |
|
WO |
|
2016/006348 |
|
Jan 2016 |
|
WO |
|
2016/051934 |
|
Apr 2016 |
|
WO |
|
2016/067885 |
|
May 2016 |
|
WO |
|
2016/076047 |
|
May 2016 |
|
WO |
|
2016/098513 |
|
Jun 2016 |
|
WO |
|
Other References
NiTi layered double hydrixide thin films for advanced
pseudocapacitor electrodes; Yaohang Gu, Zhiyi Lu, Zheng Chang,
Junfeng Liu, Xiaodong Lei, Yaping Li, and Xiaoming Sun; Journal of
Materials Chemistry, Mar. 2013 (Year: 2013). cited by examiner
.
https://pubs.acs.org/doi/pdf/10.1021/ef101150b (Year: 2010). cited
by examiner .
Extended European Search Report (Application No. 17815456.3) dated
Jan. 20, 2020. cited by applicant .
International Search Report and Written Opinion (Application No.
PCT/JP2017/022905) dated Aug. 1, 2017 (with English translation).
cited by applicant .
International Search Report and Written Opinion (Application No.
PCT/JP2017/003333) dated May 16, 2017 (with English translation).
cited by applicant .
International Search Report and Written Opinion (Application No.
PCT/JP2017/012422) dated Jun. 6, 2017 (with English translation).
cited by applicant .
International Search Report and Written Opinion (Application No.
PCT/JP2017/012427) dated Jun. 6, 2017 (with English translation).
cited by applicant .
International Search Report and Written Opinion (Application No.
PCT/JP2017/012435) dated Jun. 13, 2017 (with English translation).
cited by applicant .
Chinese Office Action, Chinese Application No. 201780038255.9,
dated Nov. 20, 2020 (8 pages). cited by applicant.
|
Primary Examiner: Stagg; Miriam
Assistant Examiner: Zhang; Rachel L
Attorney, Agent or Firm: Burr & Brown, PLLC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation application of PCT/JP2017/022905
filed Jun. 21, 2017, which claims priority to PCT/JP2017/012422
filed Mar. 27, 2017, PCT/JP2017/012427 filed Mar. 27, 2017,
PCT/JP2017/012435 filed Mar. 27, 2017, PCT/JP2017/003333 filed Jan.
31, 2017, Japanese Patent Application No. 2016-125531 filed Jun.
24, 2016, Japanese Patent Application No. 2016-125554 filed Jun.
24, 2016, and Japanese Patent Application No. 2016-125562 filed
Jun. 24, 2016, the entire contents all of which are incorporated
herein by reference.
Claims
What is claimed is:
1. A functional layer comprising a layered double hydroxide,
wherein the functional layer further comprises titania, and wherein
the layered double hydroxide is composed of a plurality of basic
hydroxide layers comprising Ni, Al, Ti and OH groups or comprising
Ni, Al and OH groups; and intermediate layers composed of anions
and H.sub.2O, each intermediate layer being interposed between two
adjacent basic hydroxide layers.
2. The functional layer according to claim 1, wherein a crystalline
structure of the titania is of an anatase type or a rutile
type.
3. The functional layer according to claim 2, wherein the ratio
I.sub.TiO2/I.sub.LDH of the peak intensity I.sub.TiO2 derived from
the titania to the peak intensity I.sub.LDH derived from the (003)
plane of the layered double hydroxide is 0.1 or more when the
surface of the functional layer is measured by X-ray
diffractometry, and wherein the I.sub.TiO2 is the intensity of the
strongest peak derived from the (101) plane in the case that the
titania is of an anatase type or the I.sub.TiO2 is the intensity of
the strongest peak derived from the (110) plane in the case that
the titania is of a rutile type.
4. The functional layer according to claim 3, wherein the ratio
I.sub.TiO2/I.sub.LDH is 10 or less.
5. The functional layer according to claim 3, wherein the ratio
I.sub.TiO2/I.sub.LDH is 1.0 or less.
6. The functional layer according to claim 1, wherein the
functional layer has a hydroxide ion conductivity.
7. The functional layer according to claim 1, wherein the
functional layer has an ion conductivity of 0.1 mS/cm or more.
8. The functional layer according to claim 1, wherein the layered
double hydroxide undergoes no change in surface microstructure and
crystalline structure when immersed in a 6 mol/L aqueous potassium
hydroxide solution containing zinc oxide in a concentration of 0.4
mol/L at 70.degree. C. for three weeks.
9. The functional layer according to claim 1, wherein the basic
hydroxide layers are composed of Ni, Al, Ti and OH groups or
composed of Ni, Al, Ti, OH groups and incidental impurities.
10. The functional layer according to claim 1, wherein the
functional layer has a helium permeability per unit area of 10
cm/minatm or less.
11. The functional layer according to claim 1, wherein the
functional layer has a thickness of 100 .mu.m or less.
12. A composite material comprising: a porous substrate; and a
functional layer according to claim 1 provided on the porous
substrate and/or embedded in the porous substrate.
13. The composite material according to claim 12, wherein the
porous substrate is composed of at least one selected from the
group consisting of ceramic materials, metallic materials, and
polymeric materials.
14. The composite material according to claim 13, wherein the
porous substrate is composed of a polymeric material, and the
functional layer is embedded over the entire region in the
thickness direction of the porous substrate.
15. The composite material according to claim 12, wherein the
composite material has a helium permeability per unit area of 10
cm/minatm or less.
16. A battery comprising, as a separator, the functional layer
according to claim 1.
17. A battery comprising, as a separator, the composite material
according to claim 12.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a functional layer including a
layered double hydroxide, and a composite material.
2. Description of the Related Art
A layered double hydroxide (hereafter also referred to LDH) is a
material having an exchangeable anions and H.sub.2O as intermediate
layers between stacked basic hydroxide layers, and is used as, for
example, catalysts, adsorbents and dispersants in polymers for
improving heat resistance to take its advantage.
The LDH has also been attractive as a material that conducts
hydroxide ions; hence, addition of the LDH to an electrolyte of an
alkaline fuel cell and a catalytic layer of a zinc air battery has
been studied. In particular, the use of a LDH as a solid
electrolyte separator for alkaline secondary batteries such as
nickel-zinc secondary batteries and zinc-air secondary batteries
has been recently proposed, and composite materials with a LDH
containing functional layer suitable for such a separator
application are known. For example, Patent Document 1
(WO2015/098610) discloses a composite material comprising a porous
substrate and a LDH containing functional layer having no water
permeability formed on and/or in the porous substrate. The LDH
containing functional layer is represented by the general formula:
M.sup.2+.sub.1-xM.sup.3+.sub.x(OH).sub.2A.sup.n-.sub.x/n.mH.sub.2O,
wherein M.sup.2+ is a divalent cation such as Mg.sup.2+, M.sup.3+
is a trivalent cation such as Al.sup.3+, A.sup.n- is an n-valent
anion such as OH.sup.-, CO.sub.3.sup.2-, n is an integer of 1 or
more, x is 0.1 to 0.4, and m is 0 or above 0. The LDH containing
functional layer disclosed in Patent Document 1 is densified to
such an extent that it has no water permeability. When the LDH is
used as a separator, it can prevent deposition of dendritic zinc
and penetration of carbon dioxide from an air electrode in zinc air
batteries that are obstacles to practical use of alkaline zinc
secondary batteries.
Unfortunately, high ionic hydroxide conductivity is required for
electrolytic solutions of alkaline secondary batteries (for
example, metal air batteries and nickel zinc batteries) including
LDHs, and thus the use of strong alkaline aqueous potassium
hydroxide solution at pH of about 14 is desired. For this purpose,
it is desirable for LDH to have high alkaline resistance such that
it is barely deteriorated even in such a strong alkaline
electrolytic solution. In this regard, Patent Document 2
(WO2016/051934) discloses a LDH containing battery that contains a
metallic compound containing a metallic element (for example, Al)
corresponding to M.sup.2+ and/or M.sup.3+ in the general formula
described above dissolved in the electrolytic solution to suppress
erosion of the LDH.
CITATION LIST
Patent Documents
Patent Document 1: WO2015/098610
Patent Document 2: WO2016/051934
SUMMARY OF THE INVENTION
The present inventors have now found that durability to an alkaline
electrolytic solution (that is, alkaline resistance) is improved by
further addition of titania into a functional layer containing a
LDH.
Accordingly, an object of the present invention is to provide a LDH
containing functional layer having high alkaline resistance, and a
composite material with the LDH containing functional layer.
One embodiment of the present invention provides a functional layer
comprising a layered double hydroxide, wherein the functional layer
further comprises titania.
Another embodiment of the present invention provides a composite
material that comprises a porous substrate and a functional layer
provided on the porous substrate and/or embedded in the porous
substrate.
Another embodiment of the present invention provides a battery
including the functional layer or the composite material as a
separator.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional view illustrating a LDH
containing composite material of one embodiment of the present
invention.
FIG. 2 is a schematic cross-sectional view illustrating a LDH
containing composite material of one another embodiment of the
present invention.
FIG. 3 is a schematic cross-sectional view illustrating an
electrochemical measurement system used in Examples 1 to 6.
FIG. 4A is an exploded perspective view of a hermetic container
used in the determination of density in Examples 1 to 6.
FIG. 4B is a schematic cross-sectional view of the measurement
system used in the determination of density in Examples 1 to 6.
FIG. 5A is a schematic view illustrating an example system of
measuring helium permeability used in Examples 1 to 6.
FIG. 5B is a schematic cross-sectional view of a sample holder and
its peripheral configuration used in the system shown in FIG.
5A.
FIG. 6 is a graph showing an X-ray diffraction pattern of a
functional layer produced in Example 3.
FIG. 7 is a BF-STEM image, an analytical pattern after FFT, and a
result of an electron analysis simulation of anatase titanium oxide
for a functional layer produced in Example 3.
FIG. 8 illustrates SEM images showing the surface microstructures
of the functional layer produced in Example 3 before immersion and
after immersion at 70.degree. C. for three weeks in an aqueous
potassium hydroxide solution.
FIG. 9 is a graph showing X-ray diffraction patterns of the
functional layer produced in Example 3 before immersion and after
immersion at 70.degree. C. for three weeks in an aqueous potassium
hydroxide solution.
FIG. 10 is an SEM image showing the surface microstructure of the
functional layer and the composite material produced in Example
6.
DETAILED DESCRIPTION OF THE INVENTION
LDH Containing Functional Layer and Composite Material
The functional layer of the present invention includes a layered
double hydroxide (LDH). The functional layer further includes
titania. As described above, high alkaline resistance that barely
exhibits the deterioration even in a strong alkaline electrolytic
solution is desired for the LDH in alkaline secondary batteries.
According to the present invention, durability to an alkaline
electrolytic solution (that is, alkaline resistance) in this regard
can be improved by further addition of titania in the LDH
containing functional layer. Meanwhile, the functional layer of the
present invention can also exhibit high ionic conductivity suitable
for the use as a separator for alkaline secondary batteries of LDH.
The present invention can accordingly provide a LDH containing
functional layer having not only high ionic conductivity but also
high alkaline resistance.
The crystalline structure of titania in the functional layer of the
present invention is preferably of anatase-type or rutile-type,
which should not be construed as limiting. Titania is preferably
contained in the functional layer in an amount capable of improving
alkaline resistance without substantially impairing ionic
conductivity of the functional layer, which should not be construed
as limiting. The content of titania can be determined by an X-ray
diffractometry. When the surface of the functional layer is
measured by the X-ray diffractometry, the ratio of the peak
intensity I.sub.TiO2 derived from titania to the peak intensity
I.sub.LDH derived from the (003) plane of the layered double
hydroxide (that is, the ratio of I.sub.TiO2/I.sub.LDH) is
preferably 0.1 or more, more preferably 0.1 to 10, further
preferably 0.1 to 1.0. In the case that titania is of an
anatase-type, I.sub.TiO2 is the peak intensity derived from the
(101) plane that is the strongest peak, the strongest peak being
typically detected at 2.theta.=24.5.degree. to 26.5.degree.. In the
case that titania is of a rutile-type, I.sub.TiO2 is the peak
intensity derived from the (110) plane that is the strongest peak,
the strongest peak being typically detected at
2.theta.=26.5.degree. to 28.5.degree.. When the
I.sub.TiO2/I.sub.LDH of the functional layer is within the above
ranges, the LDH containing functional layer has high ionic
conductivity and high alkaline resistance.
The LDH contained in the functional layer of the present invention
may have any composition. As is generally known, the LDH is
composed of a plurality of basic hydroxide layers and intermediate
layers interposed between these basic hydroxide layers. The basic
hydroxide layers are each mainly composed of metallic elements
(typically metallic ions) and OH groups. The intermediate layers of
the LDH contained in the functional layer are composed of anions
and H.sub.2O. The anions are monovalent or multivalent anions,
preferably monovalent or divalent ions. Preferably, the anions in
the LDH include OH.sup.- and/or CO.sub.3.sup.2-. The LDH in the
present invention preferably undergoes no changes of the surface
microstructure and the crystalline structure during the alkaline
resistance evaluation described above. The LDH has high ionic
conductivity based on its inherent properties, as described
above.
According to a preferred embodiment of the present invention, the
basic hydroxide layers of LDH comprise Ni, Al, Ti and OH groups, or
Ni, Al and OH groups. The intermediate layers of LDH are composed
of anions and H.sub.2O as described above. Although the alternately
stacked structure itself of basic hydroxide layers and intermediate
layers is basically the same as the generally known alternately
stacked structure of LDH, the basic hydroxide layers of LDH which
is composed of certain elements or ions mainly having Ni, Al, OH
groups and optional Ti can improve both ionic conductivity and
alkaline resistance in the functional layer. In this case, Ni in
the LDH can have the form of nickel ions. Although nickel ions in
the LDH are typically believed to be Ni.sup.2+, they may be present
in any other valence, for example, Ni.sup.3+. Al in the LDH can
have the form of nickel ions. Although aluminum ions in the LDH are
typically believed to be Al.sup.3+, they may be present in any
other valence. Ti in the LDH can have the form of titanium ions.
Although titanium ions in the LDH are typically believed to be
Ti.sup.4+, they may be present in any other valence, for example,
Ti.sup.3+. The basic hydroxide layers may contain other elements or
ions other than Ni, Al, Ti and OH groups. However, the basic
hydroxide layers preferably contain Ni, Al, OH groups and optional
Ti as main constituent elements. That is, it is preferred that the
basic hydroxide layers are mainly composed of Ni, Al, OH groups and
optional Ti. Accordingly, the basic hydroxide layers are typically
composed of Ni, Al, OH groups and optional Ti and/or incidental
impurities. For example, the basic hydroxide layers are composed of
Ni, Al, Ti and OH groups or Ni, Al, Ti, OH groups and incidental
impurities. Each of the incidental impurities is any element which
may be inevitably mixed in a manufacturing process, and it may be
mixed into the LDH from, for example, a raw material or a basic
material. The intermediate layers of LDH contained in the
functional layers are composed of anions and H.sub.2O. The anions
are monovalent or multivalent anions, preferably monovalent or
divalent ions. Preferably, the anions in the LDH include OH.sup.-
and/or CO.sub.3.sup.2-. As described above, it is impractical or
impossible to strictly specify the LDH with a general formula since
valences of Ni, Al and Ti are not necessarily confirmed. Assuming
that the basic hydroxide layers are mainly composed of Ni.sup.2+,
Al.sup.3+, Ti.sup.4+ and OH groups, the basic composition of the
corresponding LDH can be represented by the general formula:
Ni.sup.2+.sub.1-x-yAl.sup.3+.sub.xTi.sup.4+.sub.y(OH).sub.2A.sup.n-.sub.(-
x+2y)/n.mH.sub.2O, wherein A.sup.n- is an n-valent anion, n is an
integer of 1 or more, preferably 1 or 2, x is above 0 to below 1,
preferably 0.01 to 0.5, y is above 0 to below 1, preferably 0.01 to
0.5, x+y is above 0 to below 1, and m is a real number of 0 or
more, typically a real number of above 0 or 1 or more. However, it
should be understood that the general formula indicates merely the
"basic composition", and it may be replaced with other elements or
ions (including elements with other valences of the same element,
or elements or ions that may be unavoidably mixed in the
manufacturing process) to such an extent that the elements such as
Ni.sup.2+, Al.sup.3+ and Ti.sup.4+ do not impair the basic
properties of LDH.
The LDH contained in the functional layer preferably undergoes no
changes in the surface microstructure and crystalline structure
when immersed in a 6 mol/L aqueous potassium hydroxide solution
containing zinc oxide in a concentration of 0.4 mol/L at 70.degree.
C. for three weeks or 504 hours because such an LDH has high
alkaline resistance. The presence of a change in the surface
microstructure can be preferably determined by SEM (Scanning
Electron Microscopy), and the presence of a change in the
crystalline structure can be preferably determined by crystalline
structural analysis (for example, the existence and non-existence
of a shift in (003) peak derived from LDH) by XRD (X-ray
diffractometry).
The functional layer (in particular, the LDH contained in the
functional layer) has preferably ionic hydroxide conductivity. The
functional layer has preferably an ionic conductivity of at least
0.1 mS/cm, more preferably at least 0.5 mS/cm, and most preferably
at least 1.0 mS/cm. Higher ionic conductivity is preferred. The
upper limit thereof is for example, 10 mS/cm, which should not be
construed as limiting. Such high ionic conductivity is particularly
suitable for battery application. For example, it is preferred to
lower the resistance by thinning in order to put the LDH into
practical use, and providing the LDH containing functional layers
with desirably low resistance according to the embodiment is
particularly advantageous in the application of LDH as a solid
electrolyte separator for alkaline secondary batteries such as zinc
air batteries or nickel zinc batteries
Preferably, the functional layer is disposed on the porous
substrate and/or embedded into the porous substrate. That is, a
preferred embodiment of the present invention provides a composite
material comprising a porous substrate and a functional layer
disposed on the porous substrate and/or embedded into the porous
substrate. For example, as in the composite material 10 shown in
FIG. 1, a part of the functional layer 14 may be embedded in the
porous substrate 12 and the remaining part may be disposed on the
porous substrate 12. In this case, the portion of the functional
layer 14 on the porous substrate 12 is a membrane portion made of a
LDH membrane, and the portion of the functional layer 14 embedded
into the porous substrate 12 is a composite portion composed of the
porous substrate and the LDH. The composite portion is typically in
the form in which the inside of the pores of the porous substrate
12 is filled with the LDH. Also, in the case where the entire
functional layer 14' is embedded in the porous substrate 12 as the
composite material 10' shown in FIG. 2, the functional layer 14' is
mainly composed of the porous substrate 12 and the LDH. The
composite material 10' and the functional layer 14' shown in FIG. 2
can be formed by removing the membrane portion (LDH membrane) of
the functional layer 14 from the composite material 10 shown in
FIG. 1 by a known method such as polishing or cutting. In FIGS. 1
and 2, the functional layers 14, 14' are embedded only in a part of
the vicinity of the surface of the porous substrates 12, 12', but
the functional layers may be embedded in any part of the porous
substrate and over the entire part or the entire thickness of the
porous substrate.
The porous substrate in the composite material of the present
invention can preferably form the LDH containing functional layer
thereon and/or therein. The substrate may be composed of any
material and have any porous structure. Although It is typical to
form the LDH containing functional layer on and/or in the porous
substrate, the LDH containing functional layer may be formed on a
non-porous substrate and then the non-porous substrate may be
modified into a porous form by any known method. In any case, the
porous substrate has advantageously a porous structure having good
water permeability and it can deliver electrolytic solution to the
functional layer when incorporated into a battery as a separator
for the battery.
The porous substrate is composed of, preferably, at least one
selected from the group consisting of ceramic materials, metallic
materials, and polymeric materials, more preferably, at least one
selected from the group consisting of ceramic materials and
polymeric materials. More preferably, the porous substrate is
composed of ceramic materials. In this case, preferred examples of
the ceramic material include alumina, zirconia, titania, magnesia,
spinel, calcia, cordierite, zeolite, mullite, ferrite, zinc oxide,
silicon carbide, and any combination thereof. More preferred
examples include alumina, zirconia, titania, and any combination
thereof. Particularly preferred examples include alumina, zirconia
(for example, yttria-stabilized zirconia (YSZ)), and combination
thereof. Using these porous ceramics, a LDH containing functional
layer with high density can be readily formed. Preferred examples
of the metallic material include aluminum, zinc, and nickel.
Preferred examples of the polymeric material include polystyrene,
polyethersulfone, polypropylene, epoxy resin, poly(phenylene
sulfide), hydrophilized fluororesin (such as tetrafluoro resin:
PTFE), cellulose, nylon, polyethylene and any combination thereof.
All these preferred materials have high resistance to the alkaline
electrolytic solution of the battery.
Further preferably, the porous substrate is composed of the
polymeric material. The polymeric porous substrate has the
following advantageous properties; (1) high flexibility (hard to
crack even if thinned), (2) high porosity, (3) high conductivity
(thin thickness with high porosity), and (4) good manufacturability
and handling ability. Further preferred polymeric materials are
polyolefins such as, for example, polypropylene, polyethylene, and
most preferably polypropylene from the viewpoint of high resistance
to hot water, high acid resistance and high alkaline resistance, as
well as low cost. When the porous substrate is composed of the
polymeric material, it is more preferred that the functional layer
is embedded into the entire porous substrate over the thickness
(for example, most or substantially all of the pores inside the
porous substrate are filled with the LDH). The preferred thickness
of the polymeric porous substrate in this case is 5 to 200 .mu.m,
more preferably 5 to 100 .mu.m, most preferably 5 to 30 .mu.m.
Usable polymer porous substrates are microporous membranes
commercially available as separators for lithium batteries.
The porous substrate has preferably a mean pore diameter of at most
100 .mu.m, more preferably at most 50 .mu.m, for example, typically
0.001 to 1.5 .mu.m, more typically 0.001 to 1.25 .mu.m, further
more typically 0.001 to 1.0 .mu.m, particularly typically 0.001 to
0.75 .mu.m, most typically 0.001 to 0.5 .mu.m. Within these ranges,
a dense LDH containing functional layer having no water
permeability can be formed while keeping desirable water
permeability and strength as a support for the porous substrate
without the functional layer. In the present invention, the mean
pore size can be determined by measuring the largest dimension of
each pore based on the electron microscopic image of the surface of
the porous substrate. The electron microscopic image is measured at
20,000-fold magnification or more. All the measured pore sizes are
listed in order of size to calculate the average, from which the
subsequent 15 larger sizes and the subsequent 15 smaller sizes,
i.e., 30 diameters in total, are selected in one field of view. The
selected sizes of two fields of view are then averaged to yield the
average pore size. In the measurement, a dimension measuring
function in software of SEM or image analyzing software (for
example, Photoshop manufactured by Adobe) can be used.
The porous substrate has a porosity of preferably 10 to 60%, more
preferably 15 to 55%, most preferably 20 to 50%. Within these
ranges, the resulting dense LDH containing functional layer has no
water permeability while the porous substrate keeps desirable water
permeability and required strength as a support. The porosity of
the porous substrate can be preferably measured by Archimedes'
method. In the case where the porous substrate is composed of the
polymeric material and the functional layer is embedded over the
region of the porous substrate in the thickness direction, the
porosity of the porous substrate is preferably 30 to 60%, more
preferably 40 to 60%.
The functional layer preferably has no air permeability. That is,
it is preferred that the functional layer be densified with the LDH
to such an extent that it has no air permeability. In the present
specification, the phrase "having no air permeability" has the
following meaning: In the case of evaluation of air permeability by
the "density determination test" adopted in the examples described
later or a similar method, no bubbling of helium gas is observed at
one side of the measured object, i.e., the functional layer and/or
the porous substrate even if helium gas is brought into contact
with the other side in water at a differential pressure of 0.5 atm
across the thickness. By this densification, the functional layer
or the composite material as a whole selectively allows only the
hydroxide ion due to its ionic hydroxide conductivity to pass
through, and can function as separators for batteries. In the case
of the application of LDH as solid electrolyte separators for
batteries, although the bulk LDH dense body has high resistance,
the LDH containing functional layer in a preferred embodiment of
the present invention can be thinned to reduce the resistance
because the porous substrate has high strength. In addition, the
porous substrate can have high water permeability and air
permeability; hence, the electrolyte can reach the LDH containing
functional layer when used as solid electrolyte separators of
batteries. In summary, the LDH containing functional layer and the
composite material of the present invention are very useful
materials for solid electrolyte separators applicable to various
batteries, such as metal air batteries (for example, zinc air
batteries) and various other zinc secondary batteries (for example,
nickel zinc batteries).
In the functional layer or the composite material including the
functional layer, a helium permeability per unit area is preferably
10 cm/minatm or less, more preferably 5.0 cm/minatm or less, most
preferably 1.0 cm/minatm or less. The functional layer having such
a range of helium permeability has extremely high density. When the
functional layer having a helium permeability of 10 cm/minatm or
less is applied as a separator in an alkaline secondary battery,
passage of substances other than hydroxide ions can be effectively
prevented. For example, zinc secondary batteries can significantly
effectively suppress penetration of Zn in the electrolytic
solution. Since penetration of Zn is remarkably suppressed in this
way, it can be believed in principle that deposition of dendritic
zinc can be effectively suppressed in zinc secondary batteries. The
helium permeability is measured through supplying helium gas to one
surface of the functional layer to allow helium gas to pass through
the functional layer and calculating the helium permeability to
evaluate density of the functional layer. The helium permeability
is calculated from the expression of F/(P.times.S) where F is the
volume of permeated helium gas per unit time, P is the differential
pressure applied to the functional layer when helium gas permeates
through, and S is the area of the membrane through which helium gas
permeates. Evaluation of the permeability of helium gas in this
manner can extremely precisely determine the density. As a result,
a high degree of density that does not permeate as much as possible
(or permeate only a trace amount) substances other than hydroxide
ions (in particular, zinc that causes deposition of dendritic zinc)
can be effectively evaluated. Helium gas is suitable for this
evaluation because the helium gas has the smallest constitutional
unit among various atoms or molecules which can constitute the gas
and its reactivity is extremely low. That is, helium does not form
a molecule, and helium gas is present in the atomic form. In this
respect, since hydrogen gas is present in the molecular form
(H.sub.2), atomic helium is smaller than molecular H.sub.2 in a
gaseous state. Basically, H.sub.2 gas is combustible and dangerous.
By using the helium gas permeability defined by the above
expression as an index, the density can be precisely and readily
evaluated regardless of differences in sample size and measurement
condition. Thus, whether the functional layer has sufficiently high
density suitable for separators of zinc secondary batteries can be
evaluated readily, safely and effectively. The helium permeability
can be preferably measured in accordance with the procedure shown
in Evaluation A5 in Examples described later.
The functional layer has preferably a thickness of 100 .mu.m or
less, more preferably 75 .mu.m or less, further preferably 50 .mu.m
or less, particularly preferably 25 .mu.m or less, most preferably
5 .mu.m or less. Such thinning can reduce the resistance of the
functional layer. In the case where the functional layer is formed
as the LDH membrane on the porous substrate, the thickness of the
functional layer corresponds to the thickness of the membrane
portion composed of the LDH membrane. In the case where the
functional layer is formed to be embedded into the porous
substrate, the thickness of the functional layer corresponds to the
thickness of the composite portion composed of the porous substrate
and the LDH. In the case where the functional layer is formed on
and in the porous substrate, the thickness of the functional layer
corresponds to the total thickness of the membrane portion (the LDH
membrane) and the composite portion (the porous substrate and the
LDH). In any case, the above thickness leads to a low resistance
suitable for practical use in, for example, battery application.
Although the lower limit of the thickness of the LDH membrane is
not limited because it depends on the application, the thickness is
preferably 1 .mu.m or more, more preferably 2 .mu.m or more in
order to assure a certain degree of rigidity suitable for a
functional membrane such as a separator.
The LDH/titania-containing functional layer and the composite
material can be produced by any method. They can be produced by
appropriately modifying conditions of a known method for producing
LDH containing functional layers and composite materials (see, for
example, PLT 1 and 2). For example, the LDH containing functional
layer and the composite material can be produced by (1) providing a
porous substrate, (2) applying a mixed sol of alumina and titania
onto the porous substrate and then heating the sol to form an
alumina/titania layer, (3) immersing the porous substrate into an
aqueous raw material solution containing nickel ions (Ni.sup.2+)
and urea, and (4) hydrothermally treating the porous substrate in
the aqueous raw material solution to form the LDH containing
functional layer on the porous substrate and/or in the porous
substrate. The mixed sol is preferably produced by adding titanium
oxide sol into amorphous alumina sol. In particular, in Step (2),
forming the alumina/titania layer on the porous substrate can not
only produce a raw material for the LDH, but also serve as a seed
of LDH crystalline growth and uniformly form the LDH containing
functional layer that is highly densified on the surface of the
porous substrate. In addition, in Step (3), the presence of urea
raises the pH value through generation of ammonia in the solution
through the hydrolysis of urea, and gives the LDH by formation of
hydroxide with coexisting metal ions. Also, generation of carbon
dioxide in hydrolysis gives the LDH of a carbonate anion type.
In particular, a composite material in which the porous substrate
is composed of a polymeric material and the functional layer is
embedded over the porous substrate in the thickness direction is
produced by applying the mixed sol of alumina and titania to the
substrate in Step (2) in such that the mixed sol permeates into all
or most area of the interior pores of the substrate. By this
manner, most or substantially all pores inside the porous substrate
can be embedded with the LDH. Examples of preferred application
include dip coating and filtration coating. Particularly preferred
is dip coating. The amount of the deposited mixed sol can be varied
by adjusting the number of times of coating such as dip coating.
The substrate coated with the mixed sol by, for example, dip
coating may be dried and then subjected to Steps (3) and (4).
EXAMPLES
The present invention will be described in more detail by the
following examples. The functional layers and the composite
materials produced in the following examples were evaluated as
follows:
Evaluation 1: Identification of Functional Layer
The crystalline phase of the functional layer was measured with an
X-ray diffractometer (RINT TTR III manufactured by Rigaku
Corporation) at a voltage of 50 kV, a current of 300 mA, and a
measuring range of 10.degree. to 70.degree. to give an XRD profile.
The resultant XRD profile was identified with the diffraction peaks
of LDH (hydrotalcite compound) described in JCPDS card NO. 35-0964
and the diffraction peaks of TiO.sub.2 described in JCPDS card NO.
01-071-1169. The ratio of I.sub.TiO2/I.sub.LDH, that is the ratio
of the peak intensity I.sub.TiO2 derived from titania to the peak
intensity I.sub.LDH derived from the (003) plane of LDH (detected
around 2.theta.=11.42.degree.), was calculated. In this case, the
peak intensity derived from the (101) plane, which is the strongest
peak of anatase titania (detected around 2.theta.=25.16.degree.),
was employed as I.sub.TiO2.
Evaluation 2: Identification of Titania
A BF-STEM image of the functional layer was taken with a scanning
transmission electron microscope (STEM) (a brand name: JEM-ARM200
F, manufactured by JEOL). The BF-STEM image was subjected to Fast
Fourier Transform (FFT) analysis to give an analytical patter after
FFT. The resultant analytical pattern was compared with the result
of the electron analysis simulation of the anatase titanium oxide
and it was then confirmed whether the lattice constant read from
the analytical pattern after FFT roughly corresponds to the anatase
titanium oxide.
Evaluation 3: Measurement of Ionic Conductivity
The conductivity of the functional layer in the electrolytic
solution was measured with an electrochemical measurement system
shown in FIG. 3. A composite material sample S (a porous substrate
with an LDH membrane) was sandwiched between two silicone gaskets
40 having a thickness of 1 mm and assembled into a PTFE flange-type
cell 42 having an inner diameter of 6 mm. Electrodes 46 made of
#100 nickel wire mesh were assembled into a cylinder having a
diameter of 6 mm in the cell 42, and the distance between the
electrodes was 2.2 mm. The cell 42 was filled with an aqueous
electrolytic solution 44 containing 6M potassium hydroxide. Using
electrochemical measurement system (potentio-galvanostat frequency
responsive analyzers 1287A and 1255B manufactured by Solartron),
the sample was observed under the conditions of a frequency range
of 1 MHz to 0.1 Hz and an applied voltage of 10 mV, and the
resistance of the composite material sample S (the porous substrate
with LDH membrane) was determined from the intercept across a real
number axis. The resistance of the porous substrate without the LDH
membrane was also measured in the same manner. The resistance of
the LDH membrane was determined from the difference in resistance
between the composite material sample S (the porous substrate with
the LDH membrane) and the substrate. The conductivity was
determined with the resistance, the thickness, and the area of the
LDH membrane.
Evaluation 4: Evaluation of Alkaline Resistance
Zinc oxide was dissolved in a 6 mol/L aqueous potassium hydroxide
solution to yield 6 mol/L of aqueous potassium hydroxide solution
that contained zinc oxide in a concentration of 0.4 mol/L. In the
next stage, 15 mL of the resultant aqueous potassium hydroxide
solution was placed in a hermetic container made of Teflon.TM.. A
composite material having dimensions of 1 cm.times.0.6 cm was
placed on the bottom of the hermetic container such that the
functional layer faced upward, and the cover was closed. The
composite material was stored at 70.degree. C. or 30.degree. C. for
one week or 168 hours, or three weeks or 504 hours and then removed
from the hermetic container. The composite material was dried
overnight at room temperature. The microstructure of the resultant
sample was observed by SEM and the crystalline structure was
analyzed by XRD. In the analysis of crystalline structure by XRD,
if a shift of the peak (2.theta.) beyond 0.25.degree. with respect
to the (003) peak of LDH occurs after immersion in the aqueous
potassium hydroxide solution, the crystalline structure was
determined to be significantly changed.
The observation of microstructure by SEM was carried out as
follows. The surface microstructure of the functional layer was
observed at an acceleration voltage of 10 to 20 kV by a scanning
electron microscope (SEM, JSM-6610LV, manufactured by JEOL). In
addition, a cross-sectional polished surface of a functional layer
(including a membrane portion composed of the LDH membrane and a
composite portion composed of the LDH and the substrate) was
prepared with an ionic milling system (IM 4000 manufactured by
Hitachi High-Technologies Corporation) and the microstructure of
the cross-sectional polished surface was then observed by SEM under
the same conditions as the surface microstructure. The analysis of
crystalline structure was carried out by XRD as in Evaluation
1.
Evaluation 5: Elemental Analysis (EDS)
The functional layer (the membrane portion composed of the LDH
membrane and the composite portion composed of the LDH and the
substrate) was polished across the thickness for observation with a
cross-sectional polisher (CP). A field of cross-sectional image of
the functional layer (the membrane portion composed of the LDH
membrane and the composite portion composed of the LDH and the
substrate) was observed with a 10,000-fold magnification with
FE-SEM (ULTRA 55, manufactured by Carl Zeiss). The pure LDH
membrane on the substrate surface and the LDH portion (by point
analysis) inside the substrate in this cross-sectional image was
subjected to elemental analysis at an accelerating voltage of 15 kV
with an EDS analyzer (NORAN System SIX, manufactured by Thermo
Fisher Scientific Inc.).
Evaluation 6: Determination of Density
The density was determined to confirm that the functional layer had
density having no air permeability. As shown in FIGS. 4A and 4B, an
open acrylic container 130 and an alumina jig 132 with a shape and
dimensions capable of working as a cover of the acrylic container
130 were provided. The acrylic container 130 was provided with a
gas supply port 130a. The alumina jig 132 had an opening 132a
having a diameter of 5 mm and a cavity 132b surrounding the opening
132a for placing the sample. An epoxy adhesive 134 was applied onto
the cavity 132b of the alumina jig 132. The composite material
sample 136 was placed into the cavity 132b and the function layer
136b was bonded to the alumina jig 132 in an air-tight and
liquid-tight manner. The alumina jig 132 with the composite
material sample 136 was then bonded to the upper end of the acrylic
container 130 in an air-tight and liquid-tight manner with a
silicone adhesive 138 to completely seal the open portion of the
acrylic container 130. A hermetic container 140 was thereby
completed for the measurement. The hermetic container 140 for the
measurement was placed in a water vessel 142 and the gas supply
port 130a of the acrylic container 130 was connected to a pressure
gauge 144 and a flow meter 146 so that helium gas was supplied into
the acrylic container 130. Water 143 was poured in the water vessel
142 to completely submerge the hermetic container 140 for the
measurement. At this time, the air-tightness and liquid-tightness
were sufficiently kept in the interior of the hermetic container
140 for the measurement, and the functional layer 136b of the
composite material sample 136 was exposed to the internal space of
the hermetic container 140 for the measurement while the porous
substrate 136a of the composite material sample 136 was in contact
with water in the water vessel 142. In this state, helium gas was
introduced into the acrylic container 130 of the hermetic container
140 for the measurement through the gas supply port 130a. The
pressure gauge 144 and the flow meter 146 were controlled such that
the differential pressure between the inside and outside of the
functional layer 136a reached 0.5 atm (that is, the pressure of the
helium gas is 0.5 atm higher than the water pressure applied to the
porous substrate 136a). Bubbling of helium gas in water from the
composite material sample 136 was observed. When bubbling of helium
gas was not observed, the functional layer 136b was determined to
have high density with no air permeability.
Evaluation 7: Helium Permeability
A helium permeation test was conducted to evaluate the density of
the functional layer from the viewpoint of helium permeability. The
helium permeability measurement system 310 shown in FIGS. 5A and 5B
was constructed. The helium permeability measurement system 310 was
configured to supply helium gas from a gas cylinder filled with
helium gas to a sample holder 316 through the pressure gauge 312
and a flow meter 314 (digital flow meter), and to discharge the gas
by permeating from one side to the other side of the functional
layer 318 held by the sample holder 316.
The sample holder 316 had a structure including a gas supply port
316a, a sealed space 316b and a gas discharge port 316c, and was
assembled as follows: An adhesive 322 was applied along the outer
periphery of the functional layer 318 and bonded to a jig 324 (made
of ABS resin) having a central opening. Gaskets or sealing members
326a, 326b made of butyl rubber were disposed at the upper end and
the lower end, respectively, of the jig 324, and then the outer
sides of the members 326a, 326b were held with supporting members
328a, 328b (made of PTFE) each having an opening and one having a
flange. Thus, the sealed space 316b was partitioned by the
functional layer 318, the jig 324, the sealing member 326a, and the
supporting member 328a. The functional layer 318 was in the form of
a composite material formed on the porous substrate 320, and was
disposed such that the functional layer 318 faced the gas supply
port 316a. The supporting members 328a and 328b were tightly
fastened to each other with fastening means 330 with screws not to
cause leakage of helium gas from portions other than the gas
discharge port 316c. A gas supply pipe 34 was connected to the gas
supply port 316a of the sample holder 316 assembled as above
through a joint 332.
Helium gas was then supplied to the helium permeability measurement
system 310 via the gas supply pipe 334, and the gas was permeated
through the functional layer 318 held in the sample holder 316. A
gas supply pressure and a flow rate were then monitored with a
pressure gauge 312 and a flow meter 314. After permeation of helium
gas for one to thirty minutes, the helium permeability was
calculated. The helium permeability was calculated from the
expression of F/(P.times.S) where F (cm.sup.3/min) was the volume
of permeated helium gas per unit time, P (atm) was the differential
pressure applied to the functional layer when helium gas permeated
through, and S (cm.sup.2) was the area of the membrane through
which helium gas permeates. The permeation rate F (cm.sup.3/min) of
helium gas was read directly from the flow meter 314. The gauge
pressure read from the pressure gauge 312 was used for the
differential pressure P. Helium gas was supplied such that the
differential pressure P was within the range of 0.05 to 0.90
atm.
Example 1 (Comparative)
A functional layer including a LDH (not containing titania) and a
composite material were prepared and evaluated by following
procedures.
(1) Preparation of Porous Substrate
One hundred parts by weight of zirconia powder (TZ-8YS manufactured
by Tosoh Corporation), 70 parts by weight of a dispersing medium
(xylene:butanol=1:1), 11.1 parts by weight of a binder (polyvinyl
butyral: BM-2 manufactured by Sekisui Chemical Co., Ltd.), 5.5
parts by weight of a plasticizer (DOP manufactured by Kurogane
Kasei Co., Ltd.), and 2.9 parts by weight of a dispersant (Rheodol
SP-O30 manufactured by Kao Corporation) were mixed, and the mixture
was stirred to be deformed under vacuum to yield a slurry. The
slurry was shaped into a sheet on a PET membrane with a tape
shaping machine to yield a green sheet having the membrane
thickness of 220 .mu.m after drying. The green sheet was cut into
2.0 cm.times.2.0 cm.times.0.022 cm and fired at 1100.degree. C. for
two hours to yield a porous substrate made of zirconia.
The porosity of the porous substrate was determined to be 40% by
Archimedes' method. The mean pore size of the porous substrate was
also determined to be 0.2 .mu.m. In the present invention, the mean
pore size was determined by measuring the longest dimension of each
pore based on the scanning electron microscopic (SEM) image of the
surface of the porous substrate. The SEM image was observed at
20,000-fold magnification. All the measured pore sizes are listed
in order of size to calculate the average, from which the
subsequent 15 larger sizes and the subsequent 15 smaller sizes,
i.e., 30 diameters in total, are selected in one field of view. The
selected sizes of two fields of view are then averaged to yield the
average pore size. In the measurement, a dimension measuring
function in software of SEM was used.
(2) Coating of Alumina Sol on Porous Substrate
The zirconia porous substrate prepared in Procedure (1) was coated
with 0.2 mL of an amorphous alumina solution (Al-ML15 manufactured
by Taki Chemical Co., Ltd.) by spin coating. In the spin coating,
the mixed sol was dropwise added to the substrate spinning at a
rotation rate of 8,000 rpm, and the spin was then stopped after
five seconds. The substrate was placed on a hot plate heated to
100.degree. C. and dried for one minute. The substrate was then
heated at 300.degree. C. in an electric furnace. The thickness of
the layer formed by this procedure was about 1 .mu.m.
(3) Preparation of Aqueous Raw Material Solution
Nickel nitrate hexahydrate (Ni (NO.sub.3).sub.2.6H.sub.2O,
manufactured by Kanto Chemical Co., Inc.), and urea
((NH.sub.2).sub.2CO, manufactured by Sigma-Aldrich Corporation)
were provided as raw materials. Nickel nitrate hexahydrate was
weighed to be 0.015 mol/L and placed in a beaker, and ion-exchanged
water was added thereto into a total amount of 75 mL. After
stirring the solution, the urea weighed at a urea/NO.sub.3.sup.-
molar ratio of 16 was added, and further stirred to give an aqueous
raw material solution.
(4) Formation of Membrane by Hydrothermal Treatment
The aqueous raw material solution prepared in Procedure (3) and the
substrate prepared in Procedure (2) were placed in a Teflon.TM.
hermetic container (autoclave, the internal volume: 100 mL, and
covered with stainless steel jacket). The substrate was
horizontally fixed away from the bottom of the Teflon.TM. hermetic
container such that the solution was in contact with the two
surfaces of the substrate. A LDH was then formed on the surface and
the interior of the substrate by a hydrothermal treatment at a
temperature of 120.degree. C. for 24 hours. After a predetermined
period, the substrate was removed from the hermetic container,
washed with ion-exchanged water, and dried at 70.degree. C. for ten
hours to yield a LDH containing functional layer partly embedded in
the porous substrate. The thickness of the functional layer was
about 5 .mu.m (including the thickness of the portion embedded in
the porous substrate).
(5) Results of Evaluation
The resultant functional layers and composite materials were
evaluated by Evaluation 1 and 3 to 7 as described below: Evaluation
1: The resultant XRD profile determined that the functional layer
contained a LDH (hydrotalcite compound) and no titania.
Accordingly, the ratio I.sub.TiO2/I.sub.LDH was zero shown in Table
1. Evaluation 3: An ionic conductivity of the functional layer was
2.2 mS/cm shown in Table 1. Evaluation 4: The results of SEM
observation in the alkaline resistance evaluation are shown in
Table 1. No change in the microstructure of the functional layer is
observed even after immersion in the aqueous potassium hydroxide
solution at 30.degree. C. or 70.degree. C. for one week. However, a
change in the microstructure of the functional layer is observed
after immersing in the aqueous potassium hydroxide solution at
70.degree. C. for three weeks. Meanwhile, the XRD pattern in the
alkaline resistance evaluation indicate no significant change in
the crystal structure of the functional layer under all immersing
conditions. Evaluation 5: The results of EDS elemental analysis
indicate that C, Al and Ni that are constituent elements of the LDH
are detected in the LDH contained in the functional layer or in
both the LDH membrane on the substrate surface and the LDH portion
in the substrate. Al and Ni are constituent elements of the basic
hydroxide layer while C corresponds to CO.sub.3.sup.2- that is an
anion constituting the intermediate layer of LDH. Evaluation 6: The
functional layer and the composite material were confirmed to have
high density with no air permeability. Evaluation 7: Helium
permeability through the functional layer and the composite
material was 0.0 cm/minatm.
Examples 2 to 4
A functional layer and a composite material containing the LDH and
titania were prepared and evaluated as in Example 1 except that
coating of alumina/titania sol was performed instead of coating of
the alumina sol in Example 1 (2) in the following procedure.
(Coating of Alumina/Titania Sol on Porous Substrate)
An amorphous alumina solution (Al-ML15, manufactured by Taki
Chemical Co., Ltd.) and a titanium oxide sol solution (M 6,
manufactured by Taki Chemical Co., Ltd.) were mixed with Ti/Al
molar ratios of 1 (Example 2), 2 (Example 3) or 5 (Example 4) to
prepare mixed sol samples. The porous substrate made of zirconia
prepared in Procedure (1) of Example 1 was coated with 0.2 mL of
the mixed sol by spin coating. In the spin coating, the mixed sol
was dropwise added to the substrate spinning at a rotation rate of
8,000 rpm, and the spinning was then stopped after five seconds.
The substrate was placed on a hot plate heated to 100.degree. C.
and dried for one minute. The substrate was then heated at
300.degree. C. in an electric furnace. The thickness of the layer
formed by this procedure was about 1 .mu.m.
(Results of Evaluation)
Evaluations 1 to 7 were performed on the resultant functional layer
or composite material. The results were as follows. Evaluation 1:
From the resulting XRD profile, the functional layers in Examples 2
to 4 were confirmed to contain the LDH (hydrotalcite compound) and
titania. FIG. 6 illustrates X-ray diffraction patter of the
functional layer produced in Example 3. The ratio of peak
intensity, I.sub.TiO2/I.sub.LDH, was 0.1 to 0.4 as shown in Table
1. Evaluation 2: Since lattice constants read from the analytical
patterns after FFT in the functional layers of Examples 2 to 4
generally correspond to the simulated electron analysis pattern of
anatase titanium oxide, the functional layers were confirmed to
contain anatase titania. FIG. 7 illustrates the BF-STEM image and
the analytic pattern after FFT of the functional layer in Example
3. Evaluation 3: An ionic conductivity of the functional layers in
Examples 2 to 4 was 2.0 to 2.2 mS/cm equivalent to that in Examples
1 and 5, which were comparative examples. Evaluation 4: Table 1
shows the results of SEM observation in the alkaline resistance
evaluation. FIG. 8 illustrates SEM images showing the surface
microstructure of the functional layer in Example 3 before
immersion and after immersion at 70.degree. C. for three weeks in
the aqueous potassium hydroxide solution. As shown in Table 1 and
FIG. 8, no change in the microstructure of the functional layer is
observed even after immersion in the aqueous potassium hydroxide
solution at 70.degree. C. for three weeks. Meanwhile, XRD patterns
in the alkaline resistance evaluation are shown in Table 1. FIG. 9
illustrates the X-ray diffraction patterns of the functional layer
in Example 3 before immersion and after immersion at 70.degree. C.
for three weeks in the aqueous potassium hydroxide solution. As
shown in Table 1 and FIG. 9, no significant change in the
crystalline structure is observed even after immersion in the
aqueous potassium hydroxide solution at 70.degree. C. for three
weeks in all Examples 2 to 4. In summary, Examples 2 to 4 relating
to the functional layers containing the LDH and titania are
superior to Example 1 described above and Example 5 described later
relating to the functional layer containing the LDH and no titania
in alkaline resistance. In fact, the position of the (003) peak of
LDH contained in the functional layer of Examples 2 to 4 exhibits
no significant change in all the functional layers before
immersion, after immersion for one week and for three weeks in the
aqueous potassium hydroxide solution as in Table 1. Evaluation 5:
The results of EDS elemental analysis indicate that C, Al, Ti and
Ni that are constituent elements of the LDH were detected in the
LDH contained in the functional layer or in both the LDH membrane
on the substrate surface and the LDH portion in the substrate. Al,
Ni and optional Ti are constituent elements of the basic hydroxide
layer while C is derived from CO.sub.3.sup.2-, which is an anion
constituting the intermediate layer of LDH. It should be understood
that Ti is derived from titania. Evaluation 6: The functional layer
and the composite material were confirmed to have high density with
no air permeability. Evaluation 7: Helium permeability of the
functional layer and the composite material was 0.0 cm/minatm.
Example 5 (Comparative)
A functional layer including Mg/Al-containing LDH and a composite
material were prepared and evaluated by following procedures.
(1) Preparation of Porous Substrate
One hundred parts by weight of alumina powder (AES-12 manufactured
by Sumitomo Chemical Co., Ltd.), 70 parts by weight of a dispersing
medium (xylene:butanol=1:1), 11.1 parts by weight of a binder
(polyvinyl butyral: BM-2 manufactured by Sekisui Chemical Co.,
Ltd.), 5.5 parts by weight of a plasticizer (DOP manufactured by
Kurogane Kasei Co., Ltd.), and 2.9 parts by weight of a dispersant
(Rheodol SP-030 manufactured by Kao Corporation) were mixed, and
the mixture was stirred to be deformed under vacuum to yield a
slurry. The slurry was shaped into a sheet on a PET membrane with a
tape shaping machine to yield a green sheet having the membrane
thickness of 220 .mu.m after drying. The green sheet was cut into
dimensions of 2.0 cm.times.2.0 cm.times.0.022 cm and fired at
1300.degree. C. for two hours to yield a porous substrate made of
alumina. The porosity of the porous substrate was determined to be
40% by Archimedes' method. The mean pore size of the porous
substrate was also determined as in Example 1 to be 0.3 .mu.m.
(2) Spin Coating and Sulfonation of Polystyrene
A polystyrene substrate (0.6 g) was dissolved in a xylene solution
(10 mL) to prepare a spin coating solution having a polystyrene
concentration of 0.06 g/mL. The resulting spin coat solution (0.1
mL) was dropwise applied and spin-coated on the porous substrate at
a rotation rate of 8,000 rpm. The spin coating was continued for
200 seconds including the dropwise application and drying. The
porous substrate coated with the spin coating solution was
sulfonated in 95% sulfuric acid at 25.degree. C. for four days.
(3) Preparation of Aqueous Raw Material Solution
Magnesium nitrate hexahydrate (Mg(NO.sub.3).sub.2.6H.sub.2O,
manufactured by Kanto Chemical CO., Inc.), aluminum nitrate
nonahydrate (Al(NO.sub.3).sub.3.9H.sub.2O, manufactured by Kanto
Chemical CO., Inc.), and urea ((NH.sub.2).sub.2CO, manufactured by
Sigma-Aldrich Corporation) were provided as raw materials.
Magnesium nitrate hexahydrate and aluminum nitrate nonahydrate were
weighed such that a cation ratio (Mg.sup.2+/Al.sup.3+) was 2 and a
molar concentration of the total metal ions (Mg.sup.2++Al.sup.3+)
was 0.320 mol/L to be placed in a beaker. Ion-exchanged water was
added thereto into a total amount of 70 mL. After stirring the
solution, the urea weighed at a urea/NO.sub.3.sup.- molar ratio of
4 was added, and further stirred to yield an aqueous raw material
solution.
(4) Formation of Membrane by Hydrothermal Treatment
The aqueous raw material solution prepared in Procedure (3) and the
substrate prepared in Procedure (2) were placed in a Teflon.TM.
hermetic container (autoclave, the internal volume: 100 mL, and
covered with stainless steel jacket). The substrate was
horizontally fixed away from the bottom of Teflon.TM. hermetic
container such that the solution was in contact with the two
surfaces of the substrate. A LDH membrane was then formed on the
surface of the substrate by a hydrothermal treatment at a
temperature of 70.degree. C. for 168 hours (or seven days). After a
predetermined period, the substrate was removed from the hermetic
container, washed with ion-exchanged water, and dried at 70.degree.
C. for ten hours to give a LDH containing functional layer partly
embedded in the porous substrate. The thickness of the functional
layer was about 3 .mu.m (including the thickness of the portion
embedded in the porous substrate).
(5) Results of Evaluation
Evaluations 1 and 3 to 7 were performed on the resultant functional
layer or composite material. The results were as follows.
Evaluation 1: The resulting XRD profile found that the functional
layer contained a LDH (hydrotalcite compound) and no titania.
Evaluation 3: An ionic conductivity of the functional layer was 2.0
mS/cm. Evaluation 4: Table 1 illustrates the results of SEM
observation in the alkaline resistance evaluation. In Table 1, a
change in the microstructure of the functional layer was observed
even after immersion in the aqueous potassium hydroxide solution at
30.degree. C. lower than 70.degree. C. in Examples 1 to 4 for one
week (that is, even under milder alkaline condition than in
Examples 1 to 4). In addition, Table 1 illustrates the X-ray
diffraction results of the functional layer before immersion and
after immersion at 30.degree. C. for one week in the aqueous
potassium hydroxide solution. As in Table 1, a change in the
crystalline structure was observed even after immersion in the
aqueous potassium hydroxide solution at 30.degree. C. lower than
70.degree. C. in Examples 1 to 4 for one week (that is, even under
milder alkaline condition than in Examples 1 to 4). In particular,
a (003) peak of the LDH contained in the functional layer was
shifted from 2.theta.=11.70 before immersion to 2.theta.=11.44
after immersion for one week in the aqueous potassium hydroxide
solution. The shift of the (003) peak suggests that Al contained in
the LDH is eluted into the aqueous potassium hydroxide solution to
deteriorate the LDH. These results indicate that the functional
layer of Example 5 is inferior in alkaline resistance to the
functional layers of Examples 1 to 4, or the functional layers of
Examples 1 to 4 (especially, Examples 2 to 4 of the present
embodiment) are superior in alkaline resistance to the functional
layer of Example 5 of the comparative embodiment. Evaluation 5: The
results of EDS elemental analysis indicate that C, Mg and Al that
are constituent elements of the LDH are detected in the LDH
contained in the functional layer or in both the LDH membrane on
the substrate surface and the LDH portion in the substrate. Mg and
Al are constituent elements of the basic hydroxide layer while C
corresponds to CO.sub.3.sup.2- that is an anion constituting the
intermediate layer of LDH. Evaluation 6: The functional layer and
the composite material were confirmed to have high density with no
air permeability. Evaluation 7: Helium permeability through the
functional layer and the composite material was 0.0 cm/minatm.
TABLE-US-00001 TABLE 1 Evaluation of alkaline resistance Results of
Evaluation after formation of LDH XRD membrane (003) peak Coating
Results of ion shift** conditions of Results of XRD conductivity
beyond 0.25.degree. alumina/titania Presence measurement Immersing
Results of SEM observation between sol of TiO.sub.2 in Ionic
conditions Change in Change in before and Molar ratio functional
conductivity Temp. Time surface cross-sectional a- fter Ti/Al layer
I.sub.TiO2/I.sub.LDH (mS/cm) (.degree. C.) (weeks) microstructure
microstructure immersion Example 1* 0 Not 0 2.2 30 1 Not found Not
found Not found found 70 1 Not found Not found Not found 3 Found
Found Not found Example 2 1 Found 0.1 2.2 70 1 Not found Not found
Not found 3 Not found Not found Not found Example 3 2 0.2 2.1 70 3
Not found Not found Not found Example 4 5 0.4 2.0 70 3 Not found
Not found Not found Example 5* Mg/Al-containing LDH 2.0 30 1 Found
Found Found *comparative example **[(003) peak (2.theta.) before
immersion] - [(003) peak (2.theta.) after immersion] >
0.25.degree.
Example 6
A functional layer containing LDH and titania, and a composite
material were prepared with a polymeric porous substrate and
evaluated by following procedures.
(1) Preparation of Polymeric Porous Substrate
A commercially available polypropylene porous substrate having a
porosity of 50%, a mean pore size of 0.1 .mu.m and a thickness of
20 .mu.m was cut out into a size of 2.0 cm.times.2.0 cm.
(2) Coating of Alumina/Titania Sol on Polymeric Porous
Substrate
An amorphous alumina solution (Al-ML15, manufactured by Taki
Chemical Co., Ltd.) and a titanium oxide sol solution (M6,
manufactured by Taki Chemical Co., Ltd.) were mixed at Ti/Al molar
ratio of 2 to yield a mixed sol. The mixed sol was applied onto the
substrate prepared in Procedure (1) by dip coating. In dip coating,
the substrate was immersed in 100 mL of the mixed sol, pulled up
vertically and dried in a dryer at 90.degree. C. for five
minutes.
(3) Preparation of Aqueous Raw Material Solution
An aqueous raw material solution was prepared as procedure (3) in
Example 1.
(4) Formation of Membrane by Hydrothermal Treatment
The aqueous raw material solution and the dip-coated substrate were
placed in a Teflon.TM. hermetic container (autoclave, the internal
volume: 100 mL, and covered with stainless steel jacket). The
substrate was horizontally fixed away from the bottom of a
Teflon.TM. hermetic container such that the solution was in contact
with the two surfaces of the substrate. The LDH was then formed on
the surface of the substrate and in the substrate by a hydrothermal
treatment at a temperature of 120.degree. C. for 24 hours. After a
predetermined period, the substrate was removed from the hermetic
container, washed with ion-exchanged water, and dried at 70.degree.
C. for ten hours to give a LDH containing functional layer embedded
into the porous substrate.
(5) Evaluation Results
Evaluations 1 to 7 were performed on the resultant functional layer
or the composite material. The results were as follows. Evaluation
1: The resulting XRD profile found that the functional layer
contained a LDH (hydrotalcite compound) and titania. Evaluation 2:
Since lattice constant read from the analytic patterns after FFT in
the functional layers generally correspond to the electron
diffraction simulation result of anatase titanium oxide, the
functional layers were confirmed to contain anatase titania.
Evaluation 3: A conductivity of the functional layers was 2.0 mS/cm
equivalent to that in Examples 1 to 5 described above. Evaluation
4: No change in the microstructure of the functional layers was
observed even after immersion in the aqueous potassium hydroxide
solution at 70.degree. C. for 3 weeks or 7 weeks. Evaluation 5: The
results of EDS elemental analysis indicate that C, Al, Ti and Ni
that are constituent elements of the LDH are detected in the LDH
contained in the functional layer or in both the LDH membrane on
the substrate surface and the LDH portion in the substrate. Al, Ni
and optional Ti are constituent elements of the basic hydroxide
layer while C corresponds to CO.sub.3.sup.2- that is an anion
constituting the intermediate layer of LDH. Evaluation 6: The
functional layer and the composite material were confirmed to have
high density with no air permeability. Evaluation 7: Helium
permeability through the functional layer and the composite
material was 0.0 cm/minatm.
The observation of the microstructure is performed for the
resultant functional layer or composite material as follows.
(Observation of the Microstructure)
The surface microstructure of the functional layer was observed at
an acceleration voltage of 10 to 20 kV with a scanning electron
microscope (SEM, JSM-6610LV, manufactured by JEOL). In addition, a
cross-sectional polished surface of a functional layer (including a
membrane portion composed of the LDH membrane and a composite
portion composed of the LDH and the substrate) was prepared with an
ionic milling system (IM 4000 manufactured by Hitachi
High-Technologies Corporation) and the microstructure of the
cross-sectional polished surface was then observed with SEM under
the same conditions as the surface microstructure. FIG. 10
illustrates a SEM image of the cross-sectional microstructure of
the functional layer or composite material. As observed in FIG. 10,
the functional layer was embedded over the entire region in the
thickness direction of the porous substrate, or the pores of the
porous substrate were completely filled with the LDH.
* * * * *
References